1. Technical Field of the Invention
This invention relates to telecommunication systems. More particularly, and not by way of limitation, the invention is directed to a system and method of providing access to services in a telecommunications network utilizing the Session Initiation Protocol (SIP).
2. Description of Related Art
Wireless telecommunication networks are evolving from second generation (2G) circuit-switched networks to third generation (3G) packet-switched networks. A reference architecture for a 3G wireless network is being developed by the Third Generation Partnership Project (3GPP). The 3GPP network architecture uses the Session Initiation Protocol (SIP) developed by the Internet Engineering Task Force (IETF) for call setup signaling. Media is then transported through an existing IP network. The SIP standard is described in RFC 2543 which is hereby incorporated in its entirety by reference herein.
In a SIP network, users register their existence on a sub-network through a Call State Control Function (CSCF). Each user has a unique SIP ID which is an address which follows the user to different terminals. For example, when a user sits at his office desk, he can register himself as being at his desk. The desk phone sends a SIP REGISTER message with the user's unique SIP ID and the phone's hardware device ID to the CSCF so that it knows where to route the user's calls. The REGISTER message also contains a presence state that indicates the current status of the user. For example the user may designate that he is at his desk, but is currently not available.
The presence state in the REGISTER message is routed to a Presence and Instant Messaging (PIM) Server associated with the CSCF. The PIM server provides the user's presence state to other users on the network and also enables the user to monitor the presence state of other users. The user can determine the other party's presence state (for example, registered, not registered, busy, etc.) from a display such as a telephone or computer display at his desk before placing a call.
An originating user need not specify the exact destination address associated with the destination user. The 3GPP network uses aliases associated with particular users to automatically determine the identity of their registered terminals or devices, and to automatically format and deliver communications with the registered devices over an existing IP network. Thus, the 3GPP network architecture provides a centralized and independent communication control mechanism. For a registered user, the 3GPP network and associated elements keep track of the user's exact location and the identity of the user's registered terminal, and accordingly route and enable communication with that registered user over the existing IP network.
A typical service offered to subscribers in a telecommunications network is a conferencing service for setting up conference calls between three or more parties. In the 3GPP network architecture, a conference server invites the different parties to the call during call setup, and mixes and routes the media once the call is set up. The conference server may be internal or external to the CSCF network, but the user requesting the service must know the conference server's network ID. A client user, given the ID of the server, can send a message such as a SIP REFER message to the server requesting that the server initiate a conference call. For User-A to initiate a conference call to User-B and User-C, User-A sends three REFER messages to the conference server identifying the three parties to the conference call. The REFER messages may be sent directly from User-A to the conference server, or may be sent through the CSCF network. The conference server then sends out SIP INVITE messages to Users-A, B, and C. When everyone has joined the call, the conference bridge in the server performs the media mixing. This solution, however, requires that the user requesting the service know the network ID of the conference server.
A problem arises, however, when a user desires to use a service that is resident on a particular server, and the user does not know the IP address or host name of the server. For example, in the context of a conference call, the user desiring to set up the conference call may not know the network ID such as the IP address or other host name of the conference server. Without the network ID of the conference server, the user cannot communicate with the conference server to access the conferencing service and set up the conference call.
In a proposed solution, the user sends a multicast message through the network asking whether any conference servers are available. However, this is not a reliable solution since there may not be any conference servers available, or the only responding server may be too many hops away.
It would be advantageous, therefore, to have a system and method of providing access to a service in a telecommunications network when the user does not know the network ID of the server providing the service. The present invention provides such a system and method.